1. Field of the Invention
This invention relates to an electrophotographic copying apparatus, and particularly to an electrophotographic copying apparatus of the two-cycle system in which a drum-like photosensitive member, for example, is rotated through two revolutions in each copying operation.
2. Description of the Prior Art
Two methods of forming a copying image by making use of the process of electrophotography are generally known. One method produces a copying image by forming an electrostatic latent image on a sheet-like photosensitive body having a photoconductive layer, such as of ZnO or the like, developing the image with a developer including toner particles as per se well known, and then fixing the image. The other method includes forming an electrostatic latent image on a photosensitive drum, transferring a toner image onto a transfer paper after development of the latent image by toner, and then fixing this transferred image.
This invention relates to an electrophotographic copying apparatus that forms a copying image by making use of the latter method.
Because in this latter method plain paper can be used as transfer paper, and the transfer paper is light in weight and easy to handle even in multicopying, and further since a multitude of copies can be made at high speed and in a short time, this latter method is being widely put to practical use.
On the other hand, in order to continually produce satisfactory copies with repeated operations of the copying apparatus, it is necessary to restore its electrophotographic capability close to the original conditions by utilizing a cleaning means on each copying operation. Determining these conditions and implementing the cleaning operation are some of the most difficult problems presented in designing a copying apparatus.
In normal operation a toner image formed on the photosensitive body in accordance with a respective electrostatic latent image is not transferred entirely onto the transfer paper from the body; a part of the toner image is always undesireably left behind. Since this remaining or residual toner retains an electric charge and therefore adheres to the photosensitive body through electrical as well as physical coupling, simple mechanical cleaning alone is not sufficient to clean the photosensitive body. As a consequence, a preliminary treatment--such as neutralization by an electric neutralizer--becomes necessary. Furthermore, because an afterimage of the electrostatic latent image--which interferes with residual toner cleaning and, at the same time, lowers the quality of subsequently formed images--remains on the photosensitive body, it becomes necessary to eliminate this afterimage by, for example, the operative flash of a cleaning lamp.
However, even if the electrophotographic capability could be fully restored by the influence of a cleaning lamp, an electric neutralizer and a cleaning device, the cleaning device for residual toner has itself many problems associated with its use. For one thing, the surface of the photosensitive body is easily--and hence apt to be--damaged by an external force such as that associated with mechanical cleaning devices. Moreover, the extreme light weight of the residual toner renders it capable of ready scattering within the copying apparatus as a result of which components operable in forming an image--such as the discharge electrodes of a charging device and an image transferring device--are easily contaminated by the scattered toner and the copying capabilities of the apparatus are seriously diminished.
In addition, the material commonly used as a cleaning material is an animal hair or an artificial hair, the mechanical durability of which is short, and such hair of a stable nature is difficult to obtain and to process. The physical characteristics of a cleaning device also present limitations in machine design by occupying a large space in the copying apparatus, producing vibration and noise because of its high speed operation, and reducing durability of the apparatus, further lowering copy-image quality. Still further, the residual toner recovery operation, which is obtained by cleaning, is not easy to accomplish. Thus, there are many hard problems as yet unsolved.
Therefore, a proposal for a two rotation type electrophotographic copying apparatus (or an electrophotographic copying apparatus of the two-cycle system) was made as a possible solution to some of the above-mentioned problems. In this copying apparatus, a variety of operations such as charging, exposing, and developing are sequentially carried out on a photosensitive body and then a copy-image is formed in the first rotation of the photosensitive body. Preliminary operations or processes, such as the lighting of a cleaning lamp, electric corona discharging for removing or neutralizing charges remaining on the photosensitive body and on residual toner particles remaining on the body, and cleaning, are carried out during the second rotation and, preferably, the cleaning is performed by a toner developing device used in the developing process. Of course, the transferring process is carried out while the photosensitive body is rotated through its first cycle.
Thus, it becomes unnecessary to provide the copying apparatus with a separate cleaning device, noise and vibration are significantly reduced, and it further becomes possible to design a relatively compact copying apparatus.
And, as for the preliminary processing and cleaning devices of the two rotation type copying apparatus, such electrophotographic apparatus currently in use conventionally include a preliminary processing device comprising a cleaning lamp and an electric neutralizer arranged either in front (upstream) of or behind (downstream of) an electric charger.
However, such a two rotation type electrophotographic copying apparatus has a number of impediments, such as adherence of toner to equipment parts provided around the drum-type photosensitive member with increases in copying operation. This toner contamination occurs especially to the electric charger or corona charging device V (FIG. 4) and to other equipment parts used for other purposes and arranged adjacent to the electric charging device--as, for example, an anti-dew condensation plate (reference symbol 21 in FIG. 4 or M in FIGS. 2 and 7A for the photosensitive surface. In addition, toner drops onto and contaminates the photosensitive body and, should such plate be touched by an operator in changing the photosensitive body, the toner particles adhere to and contaminate the operator's hands and clothes.